Analysis of transcritical CO2 vortex tube performance using a real gas thermodynamic model

A new real gas model is developed to estimate the cold and hot exit temperatures of a vortex tube. The effect of the Bodewadt boundary layer flow is taken into account in addition to the introduction of a correction factor to account for high cold mass fractions. The model results are validated against an ideal gas model and with experimental data available in the literature for three different working fluids, namely air, R134a and carbon dioxide. The model exhibits similar results compared to the ideal gas model for air while it substantially enhances the predictions of the cold and hot exit temperatures for R134a and carbon dioxide. In addition, a parametric study is performed to test the operation of carbon dioxide under transcritical conditions. Working under transcritical conditions, liquid droplets form after the inlet gas expansion. In effect, the hot exit temperature decreases significantly below the inlet temperature. However, the cooling and heating powers can get significantly higher up to a 1 kW compared to only 90 W under subcritical conditions. Also, the exergy efficiency increases notably by at least 88.5%.